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341.
We report on the dynamics of a chromophore sequestered within the nonpolar regions of micelles and unilamellar vesicles comprised of decanoic acid/sodium decanoate. We find that there is a measurable difference in the motional dynamics of the chromophore perylene in these two nonpolar media, with the vesicle structure forming a somewhat less viscous environment than the micelle. In all cases, the chromophore reorients as a prolate rotor, implying a local environment with a nominally similar shape for both micelle and vesicle structures. These findings demonstrate that the organization of micelles is measurably different than that of bilayers. 相似文献
342.
Rathore R Abdelwahed SH Kiesewetter MK Reiter RC Stevenson CD 《The journal of physical chemistry. B》2006,110(4):1536-1540
The one-electron reduction of neutral pi-stacked di- and trifluorenes (F-2 and F-3) in HMPA, where ion association is absent, results in the formation of anion radicals in which the odd electron resides predominantly on just one of the external fluorene moieties, as established by EPR spectroscopy. However, in the case of tetrafluorene, introduction of a single electron leads to a kinetically controlled anion radical F-4(int)*- in which the odd electron undergoes rapid exchange between two central fluorene rings, where the anionic charge is partially shielded from solvation due to the presence of external fluorene rings. On a time scale of minutes, anion radical F-4(int)*- converts to a thermodynamically stabilized anion radical F-4(ext)*-, with the electron exhibiting coupling from the protons on an external fluorene moiety. The charge and spin residing on an external moiety allow efficient solvation of the anionic charge. A similar fast exchange of a single electron (probably with the involvement of quantum mechanical tunneling) among three and four internal fluorene moieties is initially observed via EPR spectroscopy in the penta- and hexafluorene derivatives, F-5 and F-6, respectively. 相似文献
343.
Stevenson CD Kiesewetter MK Reiter RC Chebny VJ Rathore R 《The journal of physical chemistry. A》2006,110(31):9602-9606
EPR studies in tetrahydrofuran, reveal that the one electron reduction of 1-(9-methyl-9H-fluoren-9-yl)-4-methylbenzene via electron transfer from cesium metal produces an anion radical that has a large affinity for the cesium cation. The affinity of this anion radical for Cs+ is so great that it will actually "suck" the Cs+ (but not Na+ or K+) right out of the grasp of 18-crown-6, leading to a cation-assisted pi-stacked complex, where the s-orbital of the metal cation is simultaneously overlapped with the pi-clouds of the phenyl and fluorenyl moieties. At ambient temperature, proton- and cesium-electron coupling constants are rapidly (on the EPR time scale) modulated as a result of the simultaneous existence of two interconverting conformers having an averaged cesium splitting (a(Cs)) of about 1.6 G. The pi-s-pi-electronic coupling can be turned on or off via the addition or removal of cesium cations. Analogous pi-s-pi-electronic coupling is observed in the 1,4-bis(9-methyl-9H-fluoren-9-yl)benzene-cesium system. 相似文献
344.
G. Sarri M. Borghesi C. A. Cecchetti L. Romagnani R. Jung O. Willi D. J. Hoarty R. M. Stevenson C. R.D. Brown S. F. James P. Hobbs J. Lockyear S. V. Bulanov F. Pegoraro 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):299-303
Multi-Mev proton beams generated by target normal sheath acceleration (TNSA) during the interaction of an ultra intense laser beam (I≥1019 W/cm2) with a thin metallic foil (thickness of the order of a few tens of microns) are particularly suited as a particle probe for laser plasma experiments. The proton imaging technique employs a laser-driven proton beam in a point-projection imaging scheme as a diagnostic tool for the detection of electric fields in such experiments. The proton probing technique has been applied in experiments of relevance to inertial confinement fusion (ICF) such as laser heated gasbags and laser-hohlraum experiments. The data provides direct information on the onset of laser beam filamentation and on the plasma expansion in the hohlraum’s interior, and confirms the suitability and usefulness of this technique as an ICF diagnostic. 相似文献
345.
A.J. Barnard D.C. Stevenson 《Journal of Quantitative Spectroscopy & Radiative Transfer》1975,15(1):123-125
The profile of the HeI 4471 Å line and its forbidden component was measured using a pulsed arc plasma (electron density 1015 cm?3, temperature 1·5 eV) as the light source. The profile is in good agreement with recent calculations in which the ion motion has been taken into account. 相似文献
346.
A series of N-methylated polyarylurea oligomers have been reduced with potassium metal in HMPA. These reductions result in the transient formation of arylurea anion radicals, which undergo reductive elimination of the urea linkages. The aryl moieties appear in the products as the anion radicals of oligoaryl systems. The reaction is intramolecular, and the sequencing in the polyaryl anion radical remains the same as in the polyarylureas due to the urea-enforced pi-pi stacking interactions. 相似文献
347.
G. Ang H. Ebenhöh F. Eisele R. Engelmann H. Filthuth W. Föhlisch V. Hepp E. Leitner W. Presser H. Schneider M. L. Stevenson T. Thouw G. Zech 《Zeitschrift für Physik A Hadrons and Nuclei》1969,228(2):151-162
The decay modesΣ ±→nπ ± γ, Σ +→pγ,Σ + →pe + e }- were studied in the 81 cm Saclay hydrogen bubble chamber. In the radiative decayΣ ±→nπ ± γ only low momentum pions which stop in the chamber were accepted. We obtain the following branching ratios: (1) $$\frac{{\Gamma {\text{(}}\sum ^{\text{ + }} \to n\pi ^ + \gamma , p_{\pi + }^*< 110{\text{ MeV/c)}}}}{{\Gamma {\text{(}}\sum ^{\text{ + }} \to n\pi ^ + )}} = (2.7 \pm 0.5) \times 10^{ - 4} ,$$ (2) $$\frac{{\Gamma {\text{(}}\sum ^ - \to n\pi ^ - \gamma , p_{\pi - }^*< 110{\text{ MeV/c)}}}}{{\Gamma {\text{(}}\sum ^ - \to n\pi ^ - )}} = (1.0 \pm 0.2) \times 10^{ - 4} ,$$ (3) $$\frac{{\Gamma {\text{(}}\sum ^ + \to p\gamma {\text{)}}}}{{\Gamma {\text{(}}\sum ^ + \to p\pi ^0 )}} = (2.1 \pm 0.3) \times 10^{ - 3} ,$$ (4) $$\frac{{\Gamma {\text{(}}\sum ^ + \to pe^ + e^ - {\text{)}}}}{{\Gamma {\text{(}}\sum ^ + \to p\pi ^0 )}} = (1.5 \pm 0.9) \times 10^{ - 5} .$$ The radiative branching ratios (1) and (2) agree well with theoretical calculations and confirm very strongly the assignmentS wave toΣ ? →nπ ? andP wave toΣ +→nπ + decay. The branching ratio (4) is based on 3 events with very low invariant masses of the electron-positron pair, being most probably radiative decays with internal conversion of theγ-ray. Combining (3) and (4) we obtain for the conversion coefficientρ: in agreement with predictions from electrodynamics. 相似文献
348.
M. Caama no P. M. Walker P. H. Regan M. Pfützner Zs. Podolyák J. Gerl M. Hellström P. Mayet M. N. Mineva A. Aprahamian J. Benlliure A. M. Bruce P. A. Butler D. Cortina Gil D. M. Cullen J. Döring T. Enqvist C. Fox J. Garcés Narro H. Geissel W. Gelletly J. Giovinazzo M. Górska H. Grawe R. Grzywacz A. Kleinböhl W. Korten M. Lewitowicz R. Lucas H. Mach C. D. O’Leary F. De Oliveira C. J. Pearson F. Rejmund M. Rejmund M. Sawicka H. Schaffner C. Schlegel K. Schmidt K. -H. Schmidt P. D. Stevenson Ch. Theisen F. Vivès D. D. Warner C. Wheldon H. J. Wollersheim S. Wooding F. Xu O. Yordanov 《The European Physical Journal A - Hadrons and Nuclei》2005,23(2):201-215
Relativistic projectile fragmentation of 208Pb has been used to produce isomers in neutron-rich, A 190 nuclides. A forward-focusing spectrometer provided ion-by-ion mass and charge identification. The detection of -rays emitted by stopped ions has led to the assignment of isomers in 188Ta, 190W, 192Re, 193Re, 195Os, 197Ir, 198Ir, 200Pt, 201Pt, 202Pt and 203Au, with half-lives ranging from approximately 10 ns to 1 ms. Tentative isomer information has been found also for 174Er, 175Er, 185Hf, 191Re, 194Re and 199Ir. In most cases, time-correlated, singles -ray events provided the first spectroscopic data on excited states for each nuclide. In 200Pt and 201Pt, the assignments are supported by - coincidences. Isomeric ratios provide additional information, such as half-life and transition energy constraints in particular cases. The level structures of the platinum isotopes are discussed, and comparisons are made with isomer systematics. 相似文献
349.
350.